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Overzichtsartikel 105
Nuclear medicine: investigation of renal function in small animal medicine
Nucleaire geneeskunde: onderzoek naar de nierfunctie bij kleine huisdieren
1
1
E. Vandermeulen, 2C. De Sadeleer, 1A. Dobbeleir, 2H. R. Ham, 1S.T. Vermeire, 1H. van Bree,
1
G. Slegers, 1 K.Y. Peremans
Department of Veterinary Medical Imaging and Small Animal Orthopedics, Faculty of Veterinary
Medicine, Ghent University, Salisburylaan 133, B-9830 Merelbeke, Belgium.
2
Department of Nuclear Medicine, University Hospital Gent, Ghent University,
De Pintelaan 185, B-9000 Ghent, Belgium.
[email protected]
ABSTRACT
Kidney function investigations in veterinary medicine are traditionally based on blood analysis (blood
urea nitrogen (BUN) and serum creatinine concentration) and / or urinalysis (urine specific gravity, proteinto-creatinine ratio or fractional excretion). Morphologic information is usually obtained by abdominal
radiography or ultrasonography. However, when more specific information on the functionality of the kidneys
is needed, nuclear medicine offers various tracers that specifically represent glomerular filtration rate, effective
renal plasma flow or functional renal mass, sometimes combining functional and morphologic data. These
procedures can be based on blood sampling techniques (non-imaging methods), or data can be obtained using
a gamma-camera (imaging methods). The most commonly used radionuclides for the examination of kidney
function in small animal medicine are discussed in this review.
SAMENVATTING
Wanneer de nierfunctie bij dieren moet bepaald worden, wordt er gewoonlijk een bloedonderzoek uitgevoerd
(voor de bepaling van de ureum- en serum/creatinineconcentratie). Het bloedonderzoek wordt vaak gecombineerd
met een urineonderzoek (voor de bepaling van het urinaire soortelijke gewicht, de urinaire eiwit/creatinineratio of
fractionele excretie). Morfologische informatie wordt verkregen via de gebruikelijke beeldvormingstechnieken, zoals
abdominale radiografie of echografie. Indien er echter meer specifieke informatie nodig is over de nierfunctie, kunnen
renale nucleaire merkers gebruikt worden. Afhankelijk van de gebruikte tracer bekomt men informatie over de
glomerulaire filtratiesnelheid (GFR), de renale doorbloeding (ERPF) of de hoeveelheid functionele niermassa.
Sommige van deze tracers geven bovendien zowel morfologische als functionele informatie. Sommige onderzoeken
zijn gebaseerd op een techniek met bloedstalen (niet-beeldvormend), terwijl men bij andere onderzoeken gebruik
maakt van een gammacamera (beeldvormend). In dit overzichtsartikel worden de meest gebruikte merkers voor
nierfunctieonderzoek bij kleine huisdieren besproken.
INTRODUCTION
Deterioration of the kidney function is a common
disease in older cats and dogs. Although the exact pathogenesis of this disease often remains unknown, the
loss of function is mostly contributed to a tubulo-interstitial condition. Clinical signs are often vague and
not necessarily related to the kidneys (e.g. weight loss,
polyuria, polydipsia). Elevation of serum creatinine
(sCreat) and blood urea nitrogen (BUN) does not become apparent until approximately 70 - 75 % of the
kidney’s functionality is lost (Finco, 1995). Besides
blood examination, urinalysis can provide insight in the
kidney function, by assessment of the presence of proteinuria or determination of the urine specific gravity.
Plain abdominal radiographs may give some information on the location, size, shape and delineation of
the kidneys, although no functional information can be
derived. Intravenous contrast urography may give more
information on functionality, but is a strenuous proce-
dure and radiographic contrast agents may be nephrotoxic. Therefore these agents must be used carefully in
patients suspected of renal disease and must be avoided in patients with severely decreased kidney function. Ultrasound provides more information on the
structure and shape of the kidneys and renal tissue, but
remains an imaging modality mainly focused on the
morphologic features of the kidneys (DiBartola, 2000).
Nuclear medicine techniques have been developed to
obtain information on the global kidney function and
furthermore, depending on the tracer used, on the individual kidney function. In the early detection of renal disease, the emphasis is mainly put on the estimation of
the glomerular filtration rate (GFR) (DiBartola, 2000).
However, the scintigraphic evaluation of the different
actions carried out by the kidneys is not limited to the
GFR. Assessment of functional tubules as a separate entity within the kidney is possible by means of a specific marker reflecting uptake in functional tubular cells.
Also, the determination of the effective renal plasma or
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blood flow can be accomplished with the appropriate
markers.
Kidney function tests with radioactive markers have
been historically of great interest in human nuclear medicine. In veterinary medicine, especially cats are prone
to kidney disease and eventually kidney failure; it is interesting to apply the findings from human medicine to
veterinary medicine. These techniques cannot only be
helpful in diagnosing declining kidney function, but
also disease progress and the effect of installed therapies,
such as a renal diet or surgery, can be monitored. Moreover, many of these tests allow the assessment of the
global kidney function as well as the individual kidney
function. The latter may be of particular interest, for instance when a surgical procedure (e.g. nephrotomy or
nephrectomy) is being considered (Barthez, 1998).
Obviously, due to the use of radioisotopes, these investigations are limited to specialized hospital settings
equipped with a nuclear medicine division.
The most commonly used renal radionuclides and
their use in dogs and cats are treated in this review.
Non-imaging methods (based on blood sampling) and
imaging methods (using a gamma-camera) for the
measurement of GFR, effective renal plasma flow
(ERPF) and assessment of the renal functional mass are
discussed.
GLOMERULAR FILTRATION RATE (GFR)
The measurement of the GFR is a good and reliable
method to assess the glomerular function of the kidneys.
It is directly related to the number of functional
nephrons in the kidneys (Gaspari, 1997; DiBartola,
2000), due to the close interaction of the glomerular and
tubular mechanisms. Early changes in renal function can
be detected by changes in the GFR, even in a non-azotaemic animal (Twardock, 1991; Lees, 2004). It is a suitable method to follow the progression (improvement or
deterioration) of kidney function over time or after installment of treatment (Bolliger, 2005), which may be of
interest for instance in patients with a low grade of
chronic kidney disease. When the individual kidney
GFR is obtained, the information may be useful prior to
nephrectomy (Barthez, 1998). Global and individual
kidney GFR methods have been developed.
The gold standard to evaluate global GFR is based
on a constant rate infusion (CRI) with inulin (Lees,
2004). Urine collection during several hours is required for this method, in order to determine the amount
of inulin eliminated from the blood through the kidneys
over the course of time. Inulin is highly suited for this
purpose, because of its pharmacokinetic characteristics:
it is freely filtrated through the glomeruli (and solely
excreted from the body through glomerular filtration),
binding to plasma proteins is absent, as is tubular secretion or reabsorption, and it is inert when passing
through the kidneys. On the other hand, there are some
disadvantages to this gold standard method. A CRI is
not practical and the collection of urine during several
hours is also very laborious and impractical. Furthermore, the determination of inulin concentration in the
Vlaams Diergeneeskundig Tijdschrift, 2011, 80
urine samples is rather costly and not straightforward.
Alternatives have been developed, using both nonradioactive (e.g. creatinine or iohexol) (Finco, 1991;
Rogers 1991; Moe, 1995; Brown, 1996; Miyamoto,
2001) and radioactive tracers (Biewenga, 1981; van
den Brom, 1981; Krawiec, 1986; Moe, 1995). All markers have similar favorable characteristics for GFR
determination, to a great extent resembling the properties of inulin. In human medicine, the choice of tracer is influenced mainly by the availability of the tracer and by work preferences. In general, iohexol
(non-radioactive) and ethylene diaminic tetraacetic
acid (EDTA) labelled with 51chromium (51Cr-EDTA)
(radioactive) are considered equivalent for GFR determination. If both are available, the ease of determination of 51Cr-EDTA may outweigh radioprotective
considerations, while sample processing of iohexol
(using HPLC) is more costly and cumbersome (Brandstrom, 1998). CRI is replaced by intravenous bolus administration of the tracer, and the clearance of the tracer from the blood can be determined with blood or
plasma samples.
For all tracers, whether radioactive or not, it is important to establish a protocol and reference values for
each tracer separately. Results from different markers
should not be extrapolated to other markers or other
species.
Considering the nuclear medicine tracers, the quantification of the GFR can be performed with non-imaging or imaging modalities.
Non-imaging methods
Non-imaging methods are based on (several) blood
samples, in which the disappearance of the tracer is
measured after a bolus injection of the tracer.
Multiple blood samples are taken at set points in
time after tracer injection. In these blood samples, the
amount of activity (arising from the presence of tracer
in the blood) is determined with a gamma well counter. The disappearance of tracer from the blood is based on clearance by glomerular filtration only, and
will give an estimation of the global GFR with the contribution from both kidneys. The activity in the blood
samples is then plotted against the progression of time,
yielding a time-activity curve (TAC). Traditionally,
the disappearance of tracer is considered to follow a
two-compartmental pharmacological model (the first
phase being a period of equilibration with the extracellular fluid, the second being the intravascular phase),
and the data are fitted using a bi-exponential function,
although other models have been investigated (Sapirstein, 1955; Moe, 1995; Heiene, 1998). Individual kidney GFR cannot be determined with this non-imaging
method.
Although this method is already easier to perform
than the gold standard inulin method, it still requires
multiple blood samples. Therefore, simplified methods – with limitation of the sample number - have
been developed, making the estimation of GFR with
the appropriate nuclear medicine tracers very feasible
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and relatively simple to perform. However, one has to
keep in mind that a decrease in sample number implies
a loss of accuracy. These simplified methods are generally considered to be acceptable for clinical use,
especially when they are established in a group of
animals with a wide range of renal functionality (Barthez, 2000). Still, the used method should be carefully
chosen, partly depending on the expected level of kidney function. When a very low kidney function is expected, it may be necessary to choose a technique based on more than 1 sample. A severely decreased
kidney function, although perhaps not difficult to diagnose, possibly hampers an accurate GFR quantification (Picciotto, 1992; Biggi, 1995; Blaufox, 1996;
Barthez, 2000).
The best-known nuclear tracer for global GFR estimation based on plasma sampling is diethylene triamine pentaacetic acid (DTPA), labelled with 99mtechnetium (99mTc-DTPA). After intravenous administration
of 99mTc-DTPA, it will quickly disperse over the circulating extracellular fluid. Even though a certain (and
variable) percentage of plasma protein binding is reported (up to 10% in dogs, unknown in cats), this does
not significantly influence the estimated GFR (Twardock, 1991; Uribe, 1992). In the dog, there is no evidence for tubular secretion or reabsorption of the tracer, making it suitable for GFR measurement (McAfee,
1981). Specific data investigating tubular tracer handling for cats are not available. A good correlation with
the gold standard inulin measurements was found using
the multi-sampling technique in dogs (Twardock, 1991)
and cats (Uribe, 1992).
A validated GFR method was established for both
dogs and cats with 12 blood samples, taken between 5
minutes and 300 minutes after the IV injection of the
tracer (Barthez, 2000). The animals included in this
study had different levels of renal function. Based on
the reference method, simplified methods were also determined. The optimal sampling times in a four-sample
protocol were 10, 20, 90 and 240 minutes after tracer
administration, yielding a good correlation with inulin
clearance (Barthez, 2000). For practical reasons, further
simplification was investigated with reduction of the
sample number to 2 (taken at 20 and 180 minutes after tracer injection) or even 1 (taken at 90 minutes after tracer injection) (Barthez, 2001). Both methods
have a good correlation when compared to the 12sample reference method. Although there is an inevitable loss of accuracy with reduction of sample number, the simplified methods are suited for clinical
practice, where the costs, efficiency and inconvenience
for the patient need to be taken into account (Barthez,
2001).
A global GFR value, determined with the non-imaging 99mTc-DTPA method, was established between
0.4 and 3.9 ml/min/kg for a group of dogs with varying renal function (normal or decreased renal function),
with an average GFR value of 2.0 ml/min/kg (± 0.9
ml/min/kg). No normal values were established in
these studies (Barthez, 2000; Barthez, 2001). A GFR
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value higher than 2.5 ml/min/kg is considered normal
in cats. Decrease of GFR to values between 1.2 and 2.5
ml/min/kg would indicate the presence of a subclinical
renal problem, whereas values below 1.2 ml/min/kg often are seen in animals that also have increased levels
of BUN and serum creatinine (Russo, 1986).
This methodology was also applied to estimate the
effect of radioactive iodine (131I) treatment of feline hyperthyroidism on the kidney function. Hyperthyroidism may temporarily support the kidney function.
After treatment of hyperthyroidism, this could result in
a decline in kidney function (Graves, 1994; Adams,
1997a). Sixty-eight percent of a group of hyperthyroid
cats with GFR values below 2.25 ml/min/kg before
treatment developed kidney failure one month after the
radioactive iodine treatment (Adams, 1997a). However, hyperthyroid cats may have normal pretreatment
99m
Tc-DTPA GFR values (above 2.25 ml/min/kg)
(Adams, 1997a) that decrease to abnormally low values
after treatment due to the cancellation of the masking
effect of excess thyroid hormone on kidney function
(Graves, 1994; Adams, 1997b).
As will be discussed further on, 99mTc-DTPA can
also be used for imaging investigations.
Despite the widespread use of 99mTc-DTPA, 51CrEDTA is considered the tracer of choice for (nuclear)
GFR studies in human medicine, especially in pediatrics (Chervu, 1982; Blaufox, 1991). The clearance of
51
Cr-EDTA has been proven to be similar to that of inulin in both dogs and humans (Favre, 1968). Solely excreted through the kidneys by glomerular filtration,
without tubular secretion or reabsorption, and with neglectable plasma protein binding, it is very suitable for
GFR studies. Studies in humans and dogs have established a very high correlation with gold standard methods (inulin and urine sampling techniques) (Garnett,
1967; Favre, 1968; Biewenga, 1981; van den Brom,
1981; Gaspari, 1997) and the tracer can be used for follow-up studies after the installment of therapies for kidney related illnesses. Since 51Cr does not emit gamma
rays suitable for imaging, it can only be used for nonimaging methods.
Until recently, this tracer had not been used in
cats. The use of 51Cr-EDTA in a group of normal and
hyperthyroid cats has been investigated. A multiple
blood sample (8 samples, taken between 5 minutes
and 240 minutes after IV tracer administration) reference method was used (Vandermeulen, 2008). Normal
GFR estimation (2.4 ml/min/kg ± 1.3 ml/min/kg) was
very similar to previously reported values obtained
with 99mTc-DTPA (Barthez, 2000). A single and 2-sample method was tested with the 8-sample method as a
reference. Both simplified methods (sampling at 48 minutes for the single sample method; first sample taken
at 30 minutes after the tracer administration, second
sample between 198 and 222 minutes for the twosample method) gave a good correlation with the reference method (r2 = 0.941 and 0.984 respectively) (Vandermeulen, 2008; Vandermeulen, 2010).
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Imaging techniques
The second method for GFR determination is based
on imaging techniques.
Contrary to 51Cr-EDTA, that lacks gamma-ray emission suitable for imaging, 99mTc-DTPA can also be
used to visualize the renal handling of the tracer with
the aid of a gamma camera. The contribution of the individual kidney to the overall GFR can be obtained,
which may be of importance, e.g. prior to a nephrectomy.
The tracer is injected as a bolus at the moment
image acquisition is started. The images are acquired
in a dynamic way, meaning that several images are obtained during a certain time frame, each lasting for a set
time. The bolus of activity can be followed in motion
on the images, as it passes through the systemic venous
circulation, the heart and lungs, to the arterial systemic circulation, and finally to the kidneys. Part of the
injected dose will be briefly accumulated in the kidneys, as the tracer will be cleared from the blood and
kidneys by glomerular filtration. The dynamic images
of the kidneys are summated, resulting in one composed image. Then, ‘Regions of Interest’ (ROI’s) are
applied over each kidney and a background area for
background activity correction. Based on the knowledge of the injected amount of activity and the number of counts obtained from the scans, it is then possible to calculate the percentage dose uptake of
99m
Tc-DTPA in each kidney separately (Krawiec, 1986).
For dogs, normal global GFR values were estimated to
be over 3.0 ml/min/kg (Krawiec, 1986; Kampa, 2003),
and the accumulation of tracer correlated well with the
clearance of inulin (Krawiec, 1986). Estimated global
GFR in normal cats calculated with this technique was
found to be 2.91 ml/min/kg (± 0.69 ml/min/kg), which
is similar to results from the gold standard technique
using a CRI of inuling with both urine and blood sampling (2.64 ml/min/kg ± 1.12 ml/min/kg) (Uribe, 1992;
Adams, 1997b). This calculated percentage uptake of
injected dose shows a good correlation with the clearance of inulin (Uribe, 1992), which improves even further when a correction is made for activity remaining
in the surrounding soft tissue (background correction).
The time-activity curves show a peak of activity in the
kidneys at approximately 3 – 4 minutes after tracer injection, followed by wash-out of the tracer from the
kidney. In cats with clinical signs of renal impairment,
it was found that this peak of activity appears only later or not at all (Uribe, 1992). Anaesthesia is often used
to restrain the animals during GFR measurements using
imaging techniques, and may influence the results, although this remains debated. A study in dogs using different sedative protocols did not reveal significant
changes in GFR when compared to GFR measurements in awake dogs (Newell, 1997). However, it has
been reported in human medicine (Lessard, 1991) and
suspected in cats that anesthesia using isoflurane may
increase GFR through systemic hemodynamic changes
(Bolliger, 2005). Although this has not yet been investigated thoroughly in cats, one needs to take into ac-
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count that sedative or anesthetic protocols, however necessary, may influence GFR measurements (Twardock,
1991; Uribe, 1992; Newell, 1997; Daniel, 1999; Bolliger, 2005). Regarding the processing of the scans, it
seems important that the method used (e.g. for ROI placement on the images) is performed in a manner that
is as standardized as possible. The error in calculations
will be reduced when the processing is always performed by the same operator, or when a (semi-) automatic computer system can be used (Kampa, 2003;
Kampa, 2006). A dynamic 99mTc-DTPA scan in a normal cat is depicted in Figure 1A and 1B. The different
frames visualize the trajectory of the tracer after intravenous injection (Figure 1A), where the image composed of the different dynamic frames also shows the
placement of the different ROI’s (Figure 1B).
Besides measurement of GFR, the gross localization
and shape of the kidneys can be visualized, although
99m
Tc-DTPA is not the nuclear tracer of choice for morphologic information (cf. infra).
The tracer can also be used for detection and evaluation of ureteral obstruction. Dynamic studies in
dogs and cats were performed before and after administration of furosemide, and the obtained TAC’s were
compared (Barthez, 1999a; Barthez, 1999b; Hecht,
2006; Hecht, 2008). Impaired tracer outflow caused by
dynamic problems was reversed after furosemide while
it persisted in cases of ureteral obstruction. This is a
simple and non-invasive method to diagnose upper
urinary tract obstruction, and although it was already
known longer in dogs (Barthez, 1999b), it has only recently been described in cats (Hecht, 2010).
Figure 1A. Fourteen frames of a dynamic 99mTc-DTPA
scan of a cat (placed in dorsal position, dorsoventral acquisition) allow tracking of the bolus of injected activity.
The arrow indicates the arrival of the tracer in the heart.
The tracer is distributed over the lungs and further into
systemic circulation, and clearly visualizes the kidneys.
(arrowheads in the last frame). (Cr = cranial, Ca = caudal, L = left, R = right).
Vlaams Diergeneeskundig Tijdschrift, 2011, 80
109
fusion and urine collection over several hours. Alternatively, two nuclear medicine tracers, 123I- or 131I-labelled ortho-iodo hippuric acid (123I-OIH and 131I-OIH)
and 99mTc-labelled mercaptoacetyl triglycine (99mTcMAG3), can be used. Both have a good correlation
with the ERPF obtained with PAH, are readily available and allow for easy ERPF determination (Chervu,
1982; Blaufox, 1996). Contrary to GFR tracers, elimination of the marker must not happen exclusively
through glomerular filtration. More important in these
investigations is a high renal extraction rate of tracer
from the blood, either by glomerular filtration or tubular secretion. A disadvantage of ERPF determination
in comparison to GFR measurement is that it is more
prone to physiologic variability. Moreover, as mentioned above, it does not represent a specific kidney function.
After tracer injection, a two-compartmental pharmacokinetic model can be seen, with a first phase of
equilibration with the extracellular fluids, and a second
intravascular phase.
Figure 1B. Summating the separate frames of a dynamic
99m
Tc-DTPA scan (cat in dorsal position, dorsoventral acquisition) provides an image on which calculations can
be performed by placing ROIs over the kidneys (ROI 1
and 2) and ROIs surrounding for background correction (ROI 3 and 4). Besides activity in the left and right
kidney, there is activity in the heart (H), as well as in the
urinary bladder (b). (Cr = cranial, Ca = caudal, L = left,
R = right).
EFFECTIVE RENAL PLASMA FLOW (ERPF)
The indications for ERPF determination are to a certain extent similar to those for GFR determination.
However, it does not represent an actual renal function,
but reflects the global and / or individual perfusion of
the kidneys (Durand, 2002) (global or individual, depending on the method used). It can be used to evaluate
the progression of kidney function over time. Amongst
others, a special indication is the assessment of kidney
perfusion after transplantation, or to detect the presence
of an upper urinary tract obstruction (Diethelm, 1980;
Dubovsky, 1995; Tulchinsky, 1996).
Similar to the determination of GFR, the ERPF can
also be determined by means of a non – imaging and
an imaging technique. The first method is based on the
disappearance of the tracer from the blood or plasma.
The ideal tracer for these studies will be almost entirely
cleared from the blood by the kidneys with one circulatory pass. This implies that the tracer should be extracted from the blood by the kidneys in a highly efficient manner, avoiding the recirculation of tracer after
passage through the kidneys. The gold standard tracer
for these investigations is para-amino hippuric acid
(PAH) (Smith, 1945). However, the determination of
PAH concentration in blood or urine samples is technically laborious and requires HPLC equipment. A
gold standard method would require constant rate in-
123
I- or 131I-OIH
123
I- or 131I-OIH is considered the (nuclear) tracer of
choice for the determination of the effective renal
blood (or plasma) flow (ERBF or ERPF) through the
kidneys (Stadalnik, 1980; Blaufox, 1991; Blaufox,
1996). Its chemical characteristics are very similar to
those of PAH. The extraction rate of OIH however is
not 100% with each circulatory pass, but goes up to approximately 95% (Daniel, 1999). The majority of the
injected OIH is excreted through tubular secretion (up
to 80 %), with the remaining 20 % being excreted
through glomerular filtration (Daniel, 1999).
Due to the presence of the iodine in the molecule,
this tracer can easily be labeled with a radioactive iodine isotope, such as 131I or 123I. A single injection method using 131I-OIH has been investigated for the determination of ERPF based on blood sampling, in dogs
as well as in cats (Barthez, 2000). Similar to the GFR
measurements, a 12-blood samples method was used as
the reference against which methods with a reduced
number of samples were compared. For dogs, the mean
ERPF determined with 131I-OIH was 134.6 ml/min (±
43.5 ml/min) or 7.0 ml/min/kg (± 3.3 ml/min/kg) when
normalized for bodyweight (Barthez 2000; Barthez,
2001). The mean ERPF for cats was found to be 28.2
ml/min (± 11.5 ml/min) or 8.7 ml/min/kg (± 4.5
ml/min/kg) (Barthez, 2000; Barthez, 2001). These studies were performed in animals with variable levels of
kidney function (including both normal, increased and
decreased values) to evaluate the method for a wide
range of measurements. Another study in normal cats
obtained an average value of 10.12 ml/min/kg (± 3.76
ml/min/kg) (Adams, 1997b).
Although the standard error increased with the reduction of samples, still a very high correlation (r2 =
0.998) was found when only 4 samples were taken (at
10, 20, 45 and 150 minutes after tracer injection) (Barthez, 2000). ERPF calculation with only 2 or one blood
110
Figure 2A. On the summated image of a dynamic 99mTcMAG3 scan of a dog (ventral position, ventrodorsal acquisition) with a renal mass, the left kidney (L) is clearly
visible. The tracer has already been cleared to the urinary bladder (b), and is still visible in the heart (H). The
right kidney contains a large non-perfused mass (M) and
is not readily identified, although some remnant kidney
tissue may be present (*). (Cr = cranial, Ca = caudal).
sample (taken at 20 and 180 minutes after tracer injection for the 2 sample method, and at 20 minutes after tracer injection for the one sample method) still yielded good correlation with the reference method (r2 =
0.994 and 0.965 respectively) (Barthez, 2001).
MAG3
MAG3 can be labeled with 99mTc, making it a very
suitable tracer for imaging procedures. Similar to 123I
(or 131I)-OIH, it can be used for calculation of the renal blood / plasma flow in veterinary medicine (Itkin,
1994; Drost, 2000). 99mTc-MAG3 is mainly excreted
through tubular secretion (up to 90%), with the remainder being cleared from the blood through glomerular filtration. A high percentage of the injected 99mTcMAG3 is bound to plasma proteins, although this is
mainly reversible. Even though the clearance of 99mTcMAG3 is lower than the clearance of 123I - OIH, still a
very high level of agreement between both tracers was
found when screening 99mTc-MAG3 for ERPF calculation in human medicine (Eshima, 1992; Daniel,
1999). Normal ERPF as determined with MAG3 in
dogs was found to be 7.0 ml/min/kg (Lora-Michiels,
2001), which is similar to the aforementioned findings
using labelled OIH. For cats, this was set at 5.3
ml/min/kg (Drost, 2003), a lower value than the findings with labelled OIH. In patients with severely impaired renal function, 99mTc-MAG3 can be used, rather
than 99mTc-DTPA for individual kidney function assessment because of its faster clearance and higher
extraction fraction (Taylor, 1990; Eshima, 1992; Drost,
2000). It will render better images even when the kidney function is low, because of lower remaining activity in the surrounding soft tissue.
When imaging procedures are performed, 99mTc-
Vlaams Diergeneeskundig Tijdschrift, 2011, 80
Figure 2B. The different frames of a 99mTc-MAG3 scan of
a dog (ventral position, ventrodorsal acquisition) with a
renal mass. At no point in time, the mass seems to be perfused. (Cr = cranial, Ca = caudal, L = left, R = right).
MAG3 is preferred over 123I (or 131I) - OIH, due to the
superior imaging qualities of 99mTc, and also due to the
high cost of the 123I used for labelling. Figure 2A depicts the summated frames of a 99mTc-MAG3 scan of a
dog with a renal mass; the separate frames of the start
of the scan can be seen in Figure 2B. This scan was performed prior to nephrectomy in order to evaluate the
perfusion of the renal mass, and to estimate the viability of the remaining kidney.
In cats it has been demonstrated that up to 16% of
the 99mTc-MAG3 clearance occurs by the liver (Drost,
2000; Drost, 2003), which may interfere with the calculation of ERPF (Drost, 2003) and may be responsible for the lower ERPF values with MAG3 in cats
when compared to results from OIH studies. It has
therefore been recommended not to use 99mTc-MAG3
for ERPF calculation based on blood sampling techniques, since no distinction can be made between tracer
cleared through the kidneys or through the liver. Imaging techniques are a better choice in cats, since they
allow correction for extra-renal activity (Drost, 2003).
A general remark that can be made for imaging
methods for ERPF measurement, similar to the remark for GFR estimation using 99mTc-DTPA scans, is
that image processing should be as much standardized
as possible in order to reduce errors in the measurements (Kampa, 2003; Kampa, 2006).
RENAL FUNCTIONAL MASS
Renal nuclear medicine imaging techniques offer a
combination of information on the morphologic aspects
of the kidneys, as well as their functionality. Although
other imaging techniques (e.g. abdominal ultrasonography, magnetic resonance imaging) give a more de-
Vlaams Diergeneeskundig Tijdschrift, 2011, 80
Figure 3A. Two acquisitions using 99mTc-DMSA of a cat,
4 hours after tracer injection. On the left image, the cat
was placed in ventral position (ventrodorsal projection);
on the right image, the cat was placed in dorsal position
(dorsoventral projection). Due to flexibility of the kidneys in the cat’s body, their position may change notably,
urging for particular care in positioning of the animals
on the camera. (L=left kidney, R=right kidney, b=urinary bladder). (Cr = cranial, Ca = caudal).
tailed image of the kidneys, each nuclear tracer suitable for imaging gives an idea of the shape, size, outline,
position or homogeneity of the kidneys. 99mTc-labelled
radiopharmaceutica in particular are highly suitable
for this purpose, because of their superior imaging
qualities, reasonable price and excellent availability.
The low energy and especially the relative short halflife of 99mTc keep the radiation burden low for patient
and practitioner. Although 99mTc-DTPA or 99mTc-MAG3
can be used for imaging studies, their presence in the
kidneys is very variable over time because of the constant clearance from the body through the kidneys.
The renal nuclear medicine agent of choice in human
medicine for obtaining morphologic information is the
chelating agent dimercaptosuccinic acid (DMSA)
(Blaufox, 1991).
99m
Tc-DMSA
99m
Tc-DMSA accumulates in the kidneys, mainly in
the proximal convoluted tubules. The renal handling
mechanisms are not entirely clarified, although a glomerular and a tubular component are involved. Because
of the specific tubular localization - leaving the lower
tubules and collecting ducts void of tracer - 99mTcDMSA scans reflect the amount of functional renal
mass, primarily located in the renal cortex (Enlander,
1974; Kawamura, 1979). After accumulation, static
image acquisition is possible several hours after tracer
injection. In dogs, the static scans are generally obtained 3 to 6 hours after tracer administration (Daniel,
1999; Kerl, 2005). The high quality scans give excellent information on the position and morphology of the
kidneys, and the relative renal function (or individual
kidney function) can be calculated (Blaufox, 1991).
The presence of a renal mass, cysts or scar after trauma
or urinary tract infection can be identified, as they will
not contain normal renal tissue and thus will not accumulate the tracer.
This tracer has only recently been introduced in feline nuclear medicine. The optimal methodology for
111
Figure 3B. A 99mTc-DMSA scan (4 hours after tracer injection) of a cat in left lateral recumbency (dorsoventral
acquisition). The activity of the kidneys overlaps, making quantification of the separate kidney function unreliable. (L = left kidney, R = right kidney, b = urinary
bladder). (Cr = cranial, Ca = caudal).
use of 99mTc-DMSA and the feasibility of applying the
tracer in cats were investigated (Vandermeulen, 2010,
unpublished data). Due to the high flexibility of the organs in the feline abdomen, the correct positioning of
the cats is imperative to obtain reliable results. Figure
3A is a dorsoventral 99mTc-DMSA scan of 1 healthy cat
in 2 different positions (ventral and dorsal position) and
shows the movability of the kidneys in the feline body.
Although the kidneys seem to move more laterally
when the cat is positioned in dorsal position, both dorsal and ventral position allow clear distinction between
both kidneys. It was also demonstrated that quantification of kidney function from scans with the animals
in lateral recumbency (with different imaging tracers)
is unreliable, although several studies describe this
position (Uribe, 1992; Drost, 2003). Due to the flexibility of the feline kidneys, activity from one kidney
may be superimposed onto the other kidney to a certain
degree (Figure 3B).
When knowledge about the relative (or split) renal
function is needed, there are some options to choose
from. However, they all require imaging modalities.
Based on the cumulative images of a 99mTc-DTPA
(Drost, 2000) or 99mTc-MAG3 scan (Eshima, 1992), the
individual contribution of the kidneys to the GFR or
ERPF can be calculated. Changes in renal activity occur rapidly, implying that the split renal function calculations also may vary over time. For instance, a
study in normal dogs reported an average day-to-day
variability of GFR estimation using 99mTc-DTPA of
8.45 % (± 4.9 %) (Kampa, 2003). 51Cr-EDTA is the nuclear tracer of choice for GFR estimation in human medicine, and allows the application of simplified plasma
clearance methods. Since it is not suited for imaging
studies, it can be combined with a 99mTc-DMSA scan,
a good representative of the functioning kidney mass.
Combining the overall estimated GFR from the 51CrEDTA investigation and the relative uptake of 99mTcDMSA yield the relative estimated GFR for the individual kidneys (Arnello, 1999; Piepsz, 2006).
CONCLUSION
When there is a need for information on a specific
renal function, various nuclear medicine tracers can be
used. Routine methods have been developed in human
112
and veterinary medicine. Depending on the desired level of accuracy, it is possible to use more simplified
methods – with a small loss in accuracy but gaining
time and effort – or more elaborate methods, mostly
used in research settings. Certain investigations do not
even necessitate the use of a gamma-camera for imaging, but can be performed by simple blood sampling.
Information on the GFR, ERPF and the estimation of
relative renal function can thus be easily obtained in
any clinical environment equipped for nuclear medicine studies. In clinical practice, the most applicable
study for kidney function investigation, for evaluation
of kidney disease progression or for pretreatment screening is GFR measurement. For this purpose, either the
combination of a reduced sampling 51Cr-EDTA GFR
estimation and 99mTc-DMSA scan (for individual kidney function) or a 99mTc-DTPA scan are the most practical methods. Only when the kidney function is expected to be very low, it may be advisable to perform
a 99mTc-MAG3 examination, due to its favorable characteristics in cases of low kidney function. For dogs,
this can then be performed by either blood sampling or
imaging. For cats, only the imaging method should be
used. It is important that, although both investigations
supply similar information, the same method should be
maintained for patient follow-up.
REFERENCES
Adams W.H., Daniel G.B., Legendre A.M., Gompf R.E.,
Grove C.A. (1997a). Changes in renal function in cats following treatment of hyperthyroidism using 131I. Veterinary Radiology and Ultrasound 38, 231-238.
Adams W.H., Daniel G.B., Legendre A.M. (1997b). Investigation of the effects of hyperthyroidism on renal function
in the cat. Canadian Journal of Veterinary Research 61,
53-56.
Arnello F., Ham H.R., Tondeur M., Piepsz A. (1999). Overall and single-kidney clearance in children with urinary
tract infection and damaged kidneys. Journal of Nuclear
Medicine 40, 52-55.
Barthez P.Y., Hornof W.J., Cowgill L.D., Neal L.A., Mickel
P. (1998). Comparison between the scintigraphic uptake
and plasma clearance of 99m-Tc-diethylenetriaminepentacetic acid (DTPA) for the evaluation of the glomerular
filtration rate in dogs. Veterinary Radiology and Ultrasound 39, 470-474.
Barthez P.Y., Wisner E.R., DiBartola S.P., Chew D.J.
(1999a). Renal transit time of 99mTc-Diethylenetriaminepentacetic acid (DTPA) in normal dogs. Veterinary Radiology and Ultrasound 40, 649-656.
Barthez P.Y., Smeak D.D., Wisner E.R., Duffey M., Chew
D.J., DiBartola S.P. (1999b). Effect of partial ureteral obstruction on results of renal scintigraphy in dogs. American Journal of Veterinary Research 60, 1383-1389.
Barthez P.Y., Chew D.J., DiBartola S.P. (2000). Effect of
sample number and time on determination of plasma clearance of technetium Tc 99m pentetate and orthoiodohippurate sodium I 131 in dogs and cats. American Journal
of Veterinary Research 61, 280-285.
Barthez P.Y., Chew D.J., DiBartola S.P (2001). Simplified
methods for estimation of 99mTc-pentetate and 131I-or-
Vlaams Diergeneeskundig Tijdschrift, 2011, 80
thoiodohippurate plasma clearance in dogs and cats. Journal of Veterinary Internal Medicine 15, 200-208.
Biewenga W.J., van den Brom W.E. (1981). Assessment of
glomerular filtration rate in dogs with renal insufficiency:
analysis of the 51Cr-EDTA clearance and its relation to the
plasma concentrations of urea and creatinine. Research in
Veterinary Science 30, 158-60.
Biggi A., Viglietti A., Farinelli M.C., Bonada C., Camuzzini
G. (1995). Estimation of glomerular filtration rate using
chromium-51 ethylene diamine tetra-acetic acid and technetium-99m diethylene triamine penta-acetic acid. European Journal of Nuclear Medicine 22, 532 – 536.
Blaufox M.D. (1991). Procedures of choice in renal nuclear
medicine. Journal of Nuclear Medicine 32, 1301-1309.
Blaufox M.D., Aurell M., Bubeck B., Fommei E., Piepsz A.,
Russell C., Taylor A., Thonsen H.S., Volteranni D. (1996).
Report of the radionuclides in nephrourology committee
on renal clearance. Journal of Nuclear Medicine 37, 18831890.
Bolliger C., Walshaw R., Kruger J.M., Rosenstein D.S.
Richter M.A., Hauptman J.G. Mauer W.A. (2005). Evaluation of the effects of nephrotomy on renal function in
clinically normal cats. American Journal of Veterinary Research 66, 1400-1407.
Brandstrom E., Grzegorczyk A., Jacobsson L., Friberg P.,
Lindahl A., Aurell M. (1998). GFR measurement with iohexol and 51Cr-EDTA. A comparison of the two favoured
GFR markers in Europe. Nephrology Dialysis Transplantation 13, 1176-1182.
Brown S.A., Finco D.R., Boudinot F.D., Wright J., Taver
S.L., Cooper T. (1996). Evaluation of a single injection
method, using iohexol, for estimating glomerular filtration
rate in cats and dogs. American Journal of Veterinary Research 57, 105-110.
Chervu L.R., Blaufox M.D. (1982). Renal radiopharmaceuticals - an update. Seminars in Nuclear Medicine 12, 224245.
Daniel G.B., Mitchell S.K., Mawby D., Sackman J.E.,
Schmidt D. (1999). Renal nuclear medicine: a review. Veterinary Radiology and Ultrasound 40, 572-587.
DiBartola S.P., Rutgers H.C., Zack P.M., Tarr M.J. (1987).
Clinicopathologic findings associated with chronic renal
disease in cats: 74 cases (1973-1984). Journal of the
American Veterinary Medical Association 190, 1196-1202.
Diethelm A.G., Dubovsky E.V., Whelchel J.D., Hartley
M.W., Tauxe W.N. (1980). Diagnosis of impaired renal
function after kidney transplantation using renal scintigraphy, renal plasma flow and urinary excretion of hippurate. Annals of Surgery 191, 604-616.
Drost W.T., Henry G.A., Meinkoth J.H., Woods J.P., Payton
M.E., Rodebusch C. (2000). The effects of a unilateral ultrasound-guided renal biopsy on renal function in healthy
sedated cats. Veterinary Radiology and Ultrasound 41, 5762.
Drost W.T., McLoughlin M.A., Mattoon J.S., Lerche P., Samii V.F., DiBartola S.P., Chew D.J., Barthez P.Y. (2003).
Determination of extrarenal plasma clearance and hepatic
uptake of technetium-99m-MAG3 in cats. American Journal of Veterinary Research 64, 1076-1080.
Dubovsky E.V., Russell C.D., Erbas B. (995). Radionuclide
evaluation of renal transplants. Seminars in Nuclear Medicine 25, 49-59.
Durand E., Prigent A. (2002). The basics of renal imaging
and function studies. Quaterly Journal of Nuclear Medicine 46, 249 – 267.
Vlaams Diergeneeskundig Tijdschrift, 2011, 80
Enlander D., Weber P.M., dos Remedios L.V. (1974). Renal
cortical imaging in 35 patients: superior quality with 99mTcDMSA. Journal of Nuclear Medicine 15, 743-749.
Eshima D., Taylor A., Jr. (1992). Technetium-99m (99mTc)
mercaptoacetyltriglycine: update on the new 99mTc renal tubular function agent. Seminars in Nuclear Medicine 22,
61-73.
Favre H.R., Wing A.J. (1968). Simultaneous 51Cr edetic
acid, inulin, and endogenous creatinine clearances in 20
patients with renal disease. British Medical Journal 1, 8486.
Finco D.R., Brown S.A., Crowell W.A., Barsanti J.A. (1991).
Exogenous creatnine clearance as a measure of glomerular filtration rate in dogs with reduced renal mass. American Journal of Veterinary Research 52, 1029-1032.
Finco D.R., Brown S.A., Vaden S.L., Ferguson D.C. (1995).
Relationship between plasma creatinine concentration and
glomerular filtration rate in dogs. Journal of Veterinary
Pharmacology and Therapeutics 18, 418-421.
Garnett E.S., Parsons V., Veall N. (1967). Measurement of
glomerular filtration-rate in man using a 51Cr-edetic-acid
complex. Lancet 1, 818-819.
Gaspari F., Perico N., Remuzzi G. (1997). Measurement of
glomerular filtration rate. Kidney International Supplement 63, S151-154.
Graves T.K., Olivier N.B., Nachreiner R.F., Kruger J.M.,
Walshaw R., Stickle R.L. (1994). Changes in renal function associated with treatment of hyperthyroidism in cats.
American Journal of Veterinary Research 55, 1745-1749.
Hecht S., Daniel G.B., Mitchell S.K. (2006). Diuretic renal
scintigraphy in normal dogs. Veterinary Radiology and Ultrasound 47, 602-608.
Hecht S., Lane I.F., Daniel G.B., Morandi F., Sharp D.E.
(2008). Diuretic renal scintigraphy in normal cats. Veterinary Radiology and Ultrasound 49, 589-594.
Hecht S., Lawson S.M., Lane I.F., Sharp D.E., Daniel G.B.
(2010). 99mTc-DTPA diuretic renal scintigraphy in cats
with nephrourolithiasis. Journal of Feline Medicine and
Surgery 12, 423 – 430.
Heiene R., Moe L. (1998). Pharmacokinetic aspects of measurement of glomerular filtration rate in the dog: a review.
Journal of Veterinary Internal Medicine 12, 401-414.
Itkin R.J., Krawiec D.R., Twardock A.R, Gelberg H.B.
(1994). Quantitative renal scintigraphic determination of
effective renal plasma flow in dogs with normal and abnormal renal function, using 99mTc-mercaptoacetyltriglycine. American Journal of Veterinary Research 55,
1660-1665.
Kampa N., Boström I., Lord P., Wennstrom U., Ohagen P.,
Maripuu E. (2003) Day-to-day variability in GFR in normal dogs by scintigraphic technique. Journal of Veterinary
Medicine. A, Physiology, pathology, clinical medicine 50,
37-41.
Kampa N., Lord P., Maripuu E. (2006). Effect of observer
vairability on glomerular filtration rate measurement by renal scintigraphy in dogs. Veterinary Radiology and Ultrasound 47, 212 – 221.
Kawamura J., Hosokawa S., Yoshida O. (1979). Renal function studies using 99mTc-dimercaptosuccinic acid. Clinical Nuclear Medicine 4, 39-46.
Kerl M.E., Cook C.R. (2005). Glomerular filtration rate and
renal scintigraphy. Clinical Techniques in Small Animal
Practice 20, 31-8.
Krawiec D.R., Badertscher R.R., Twardock A.R., Rubin
S.I., Gelberg, H.B. (1986). Evaluation of 99mTc-DTPA
113
nuclear imaging for quantitative determination of the GFR
in dogs. American Journal of Veterinary Research 47,
2175 - 2179.
Lees, G.E. (2004). Early diagnosis of renal disease and renal failure. Veterinary Clinics of North America: Small
Animal Practice 34, 867-885.
Lessard M.R., Trépanier C.A. (1991). Renal function and hemodynamics during prolonged isoflurane-induced hypotension in humans. Anesthesiology 74, 860 - 865.
Lora-Michiels M., Anzola K., Amaya G., Solano M. (2001).
Quantitative and qualitative scintigraphic measurement of
renal function in dogs exposed to toxic doses of gentamycin. Veterinary Radiology and Ultrasound 42, 553 561.
McAfee J.G., Grossman Z.D., Gagne G., Zens A.L., Subramanian G., Thomas F.D., Fernandez P., Roskopf M.L.
(1981). Comparison of renal extraction efficiencies for radioactive agents in the normal dog. Journal of Nuclear
Medicine 22, 333-338.
Miyamoto K. (2001) Use of plasma clearance of iohexol for
estimating GFR in cats. American Journal of Veterinary
Research 62(4), 572 - 575.
Moe L., Heiene R. (1995). Estimation of GFR in dogs with
99m-Tc-DTPA and iohexol. Research in Veterinary
Science 58, 138-143.
Newell S.M., Ko J.C., Ginn P.E., Heaton-Jones T.G., Hyatt
D.A., Cardwell A.L., Mauragis D.F., Harrison J.M. (1997).
Effects of three sedative protocols on glomerular filtration
rate in clinically normal dogs. American Journal of Veterinary Research 58, 446-450.
Picciotto G., Cacace G., Cesana P., Mosso R., Ropolo R., De
Filippi P.G. (1992). Estimation of chromium-51 ethylene
diamine tetra-acetic acid plasma clearance: a comparative
assessment of simplified techniques. European Journal of
Nuclear Medicine 19, 30 – 35.
Piepsz A., Tondeur M., Ham H. (2006). Revisiting normal
(51)Cr-ethylenediaminetetraacetic acid clearance values in
children. European Journal of Nuclear Medicine and Molecular Imaging 33, 1477-1482.
Rogers K.S., Komkov A., Brown S.A., Lees G.E., Hightower D., Russo E.A. (1991). Comparison of four methods
of estimating GFR in cats. American Journal of Veterinary
Research 52, 961 - 964.
Russo E.A., G.E. Lees, Hightower D. (1986). Evaluation of
renal function in cats, using quantitative urinalysis. American Journal of Veterinary Research 47, 1308-1312.
Sapirstein L.A., Vidt D.G., Mandel M.J., Hanusek G. (1955)
Volumes of distribution and clearances of intravenoudsly
injected creatinine in the dog. American Journal of Physiology 181, 330 – 336.
Smith H.W., Finkelstein N., Aliminosa L., Crawford B.,
Graber M. (1945). The Renal Clearances of Substituted
Hippuric Acid Derivatives and Other Aromatic Acids in
Dog and Man. Journal of Clinical Investigation 24, 388404.
Stadalnik R.C., Vogel J.M., Jansholt A.L., Krohn K.A., Matolo N.M., Lagunas-Solar M.C., Zielinski F.W. (1980). Renal clearance and extraction parameters of ortho-iodohippurate (I-123) compared with OIH(I-131) and PAH.
Journal of Nuclear Medicine 21, 168-170.
Taylor A. Jr., Ziffer J.A., Eshima D. (1990). Comparison of
Tc-99m MAG3 and Tc-99m DTPA in renal transplant patients with impaired renal function. Clinical Nuclear Medicine 15, 371-378.
Tulchinsky M., Dietrich T.J., Eggli D.F., Yang H.C. (1996).
114
Vlaams Diergeneeskundig Tijdschrift, 2011, 80
Technetium - 99m - MAG3 scintigraphy in acute renal failure ofter transplantation: a marker of viability and prognosis. Journal of Nuclear Medicine 38, 475-478.
Twardock A.R., Krawiec D.R., Lamb C.R. (1991). Kidney
scintigraphy. Seminars in Veterinary Medicine and Surgery (Small Animal) 6, 164-169.
Uribe D., Krawiec D.R., Twardock A.R., Gelberg H.B.
(1992). Quantitative renal scintigraphic determination of
the GFR in cats with normal and abnormal kidney function, using 99mTc-DTPA. American Journal of Veterinary
Research 53, 1101-1107.
van den Brom W.E, Biewenga W.J. (1981). Assessment of
glomerular filtration rate in normal dog: analysis of the
51Cr-EDTA clearance and its relation to several endogenous parameters of glomerular filtration. Research in Veterinary Science 30, 152-157.
Vandermeulen E., van Hoek I, De Sadeleer C., Piepsz A.,
Ham H.R., Bosmans T., Dobbeleir A., Daminet S., Peremans K. (2008). A single sample method for evaluating
51chromium-ethylene diaminic tetraacetic acid clearance
in normal and hyperthyroid cats. Journal of Veterinary Internal Medicine 22, 266-272.
Vandermeulen E., De Sadeleer C., Piepsz A., Ham H.R.,
Dobbeleir A., Van Hoek I., Daminet S., Slegers G., Peremans K. (2010). Determination of optimal sampling times
for a two blood sample clearance method using 51CrEDTA in cats. Journal of Feline Medicine and Surgery, in
press.
Uit het verleden
REIN EN ONREIN VOEDSEL
Van oudsher waarderen allerhande menselijke maatschappijen de dieren in termen van wild en tam, nuttig en nutteloos of zelfs schadelijk, maar vooral als eetbaar en oneetbaar. Dit laatste onderscheid werd dikwijls in een religieuze
context ingebed, waardoor het een dwingend karakter kreeg. Zeer bekend zijn de oudtestamentische regels zoals die
in het boek Leviticus (hoofdstuk 11) worden uiteengezet: En de Heere sprak tot Mozes en tot Aäron, zeggende tot hen;
spreekt tot de kinderen Israëls, zeggende: dit is het gedierte dat gij eten zult uit alle beesten die op aarde zijn. De voorschriften zijn zeer gedetailleerd en expliciet. Zijn acceptabel: beesten met in twee gespleten klauwen die ook herkauwen (exclusief dus varkens die niet herkauwen, of herkauwers zoals kamelen en caecotrofe konijnen en hazen die geen
gespleten klauwen hebben), in het water levende dieren met vinnen en ook schubben en zelfs sommige insecten, zoals
sprinkhanen. Niet eetbaar zijn een twintigtal met naam opgesomde vogelsoorten waaronder arenden, haviken, kraaien,
raven en verder ook nog gedierte dat op of onder de aarde kruipt. Uiterst streng is het verbod op het eten van aas (doodgevonden dieren) en alles wat daarmee in aanraking komt.
Deze verboden en regels leven in varianten en aanvullingen nog door in de voorschriften voor het kosjer en halal
voedsel (rein in religieuze zin), de wijze van slachten inbegrepen. In het christendom verdween het onderscheid tussen rein en onrein voedsel mettertijd. In de vroege middeleeuwen vervaardigde de kerk nog verboden uit op het eten
van kraaiachtigen, ooievaars, hazen, bevers en paarden. Vooral het taboe op het eten van paardenvlees is welbekend.
Het zou gebaseerd zijn op de betekenis van dit dier in sommige heidense rituelen. Het is zoals ook andere taboes sterk
geografisch gedetermineerd. Zo is paardenvlees in Japan een delicatesse (basashi).
Van belang voor de lokale West-Europese tradities is vooral het volgende. Tijdens de reformatie en haar katholieke
tegenhanger, de contrareformatie (jaren 1500–1600), veranderde de houding van de kerken. Voedingsgewoonten hadden voortaan niets met religie te maken. Het onderscheid tussen rein en onrein was door de komst van Christus opgeheven, zo werd gesteld. Voor de reinen van geest waren immers alle dingen rein. Alleen sommige sektariërs hielden
vast aan de leer dat het bijvoorbeeld zondig was varkensvlees te eten. Ze steunden hiervoor op het verbod uit het oude
testament of op het verhaal van Jezus die boze geesten in varkens had doen varen.
Dit betekende echter geenszins dat de voedingsgewoonten meteen veranderden. Naast inertie en gewoonte bleven
immers heel wat andere subjectieve factoren onverkort een rol spelen in de aanvaardbaarheid van diverse dieren (of van
dieren in het algemeen) als voedselbron, maar dat is een ander verhaal.
Bronnen
Bijbel, dat is de gansche Heilige Schrift (Staten-bijbel) en Thomas, K., Man and the Natural World, changing attitudes in England (1500 – 1800), Lane, London, 1983. Vertaald als Het verlangen naar de Natuur, Agon, Amsterdam,
1990.
Zie ook: Devriese L. (2008). Varkensvlees: taboe of schaars. Vlaams Diergeneeskundig Tijdschrift 77, 455.
Luc Devriese